1. Field of the Invention
The present invention relates generally to the field of coupling systems for use in surgical implants. More particularly, the present invention relates to such systems for use in orthopedic rod fixation systems.
2. Related Art
Bone stabilization/fixation devices to align or position bones have been used for some time. Such devices have been used to align or position specific vertebrae, or a specific region of the spine. Typically, such devices utilize a coupling assembly to connect or link two or more surgical screws and/or pedicle screws together to stabilize the bone and/or joint around which the screws are fixed. Conventional coupling assemblies are typically comprised of a relatively rigid member, such as a plate or a rod, that is used to couple or join adjacent structures or parts of the anatomy. Once the coupled structures are spatially fixed in position, surgical procedures can be completed and healing can proceed.
The present inventor has found, however, that such conventional surgical and/or pedicle screw coupling systems have several drawbacks. For example, such systems are rather large and bulky, which can result in increased tissue damage in and around the surgical site, resulting both from installation of the coupling system during surgery and from implant induced, post-operative tissue irritation and erosion. The relative bulk of prior art devices can be particularly troublesome in supra-fascial applications.
Some prior art coupling systems have a rod-receiving device that is delivered to the surgeon already coupled or attached to the head of the surgical screw, which poses two challenges: 1) this prevents certain surgical maneuvers (e.g. placing the screws prior to interbody work); and, 2) increases the carrying cost of the inventory. Furthermore, traditional coupling systems do not allow for varying the rod stiffness along a multi-segmented construct; certain indications may require a stiff rod over one segment and a flexible rod over another.
Further, traditional systems inherently possess an inability to easily extend a fusion: e.g., in a revision procedure, the existing rod would need to be either completely removed and replaced with a new rod or cut in vivo. In addition, some of the prior art coupling systems include locking components (e.g., set screws and the like) that must all be carefully assembled together during the surgical procedure. Further, many traditional surgical screw system designs complicate or even preclude the ability to be placed percutaneously over a guide wire, which makes these systems more difficult to install and maneuver during surgical procedures, including minimally invasive procedures.
Furthermore, many prior art devices require that the rod be attached to the coupling device after the screw is inserted in the bone, which can be disadvantageous at times, whereas the option to assemble the rod to the coupling device outside the wound may prove valuable. Also, existing coupling systems often necessitate simultaneous locking of all components, which prevents the ability to properly compress a coupling system along the rod because the angle relative to the surgical screw would change.
Furthermore, predicate technology necessitates bending of the rod for multi-segmented constructs. Rod bending is not only cumbersome to perform, but invariably results in an unintended stress applied to the bones.